As a method for producing FRP, there is known an RTM method that molds an FRP molded article having a predetermined thickness by disposing a reinforcing fiber substrate in a mold cavity formed by an upper mold and a lower mold, pressurizing the molds to clamp the molds, injecting and impregnating a pressured matrix resin into the reinforcing fiber substrate, and then hardening the impregnated resin. As a technology for molding a particularly large FRP structural body using the RTM method that uses an upper mold and a lower mold, there has been proposed a multipoint injection technology in which in order to achieve the purpose of favorably injecting and impregnating a matrix resin into a reinforcing fiber substrate over a large area, the resin is injected substantially simultaneously through a plurality of sites (e.g., Patent document 1).
Besides the RTM method that uses an upper mold and a lower mold as described above, there is known another RTM method that uses a bag material. In this method, instead of an upper mold, a bag material, such as a film made of resin, is used, and a reinforcing fiber substrate set on a lower mold is covered with the bag material, and the bag material and the lower mold are tightly closed with a seal material, the inside covered with the bag material is depressurized by vacuum suction, and, utilizing the depressurized state, a matrix resin is injected into the inside so as to impregnate into a reinforcing fiber substrate, and then the impregnated resin is hardened. Furthermore, in the RTM method that uses a bag material, there is known a technology in which after resin impregnation, surplus resin in the reinforcing fiber substrate is sucked and removed through a suction line disposed inside the bag material so as to control the Vf (e.g., Patent document 2).
Furthermore, in the RTM method that uses an upper mold and a lower mold as described above, it is usual to inject and impregnate a pressurized matrix resin into a reinforcing fiber substrate during a state in which an internal dimension height of a mold cavity has been adjusted so that the thickness of the reinforcing fiber substrate is substantially equal to the thickness of a molded article that is to be obtained by molding, a so-called product. However, with regard to the RTM method that uses an upper mold and a lower mold, as a technology for applying the method to the molding of a large-size FRP structural body, there is known a technology in which, in a state where a reinforcing fiber substrate has been disposed within a mold cavity formed by an upper mold and a lower mold and an internal dimension height of a mold cavity has been made larger than the thickness of the product, a resin is injected and impregnated into the reinforcing fiber substrate, and, after that, the resin injected and impregnated in surplus into the reinforcing fiber substrate is sucked and removed, and at least one of the upper mold and the lower mold is pressurized toward the other so as to control the internal dimension height of the mold cavity so that the thickness of the reinforcing fiber substrate becomes equal to the thickness of the product, and, in that state, the resin is hardened (e.g., Patent document 3). Use of the technology disclosed in Patent document 3 makes it possible to efficiently produce tabular molded articles that have a large size, a large thick-walled, and a high Vf.
Furthermore, a technology that uses thermal expansion of a rubber or an elastomer as a supply source of pressure needed at the time of molding of FRP is known (e.g., Patent documents 4 and 5). According to the technology disclosed in Patent document 4, a rubber layer is caused to expand by heating so as to extrude surplus resin, so that it becomes possible to produce a structural body in which a stable amount of resin has been deposited and solidified. According to the technology disclosed in Patent document 5, it becomes possible to produce large-size molded articles in a prepreg molding method without using an autoclave apparatus.